The invention relates to a hydroformylation process that employs a organopolyphosphite ligand and an organomonophosphite ligand.
US 2010/0069680 teaches that hydroformylation reactions featuring a mixture of a chelating bisphosphite and a bulky monophosphite ligand, where the bisphosphite is employed at a less than stoichiometric amount relative to rhodium and the process is operated in the negative order region of the carbon monoxide partial pressure curve, can provide improved control of the product isomer ratio. This technology can allow practitioners to tailor their processes to meet shifting market and customer demands. However, when the components of such a mixed ligand system are initially charged to a reactor, the bisphosphite ligand rapidly coordinates to a portion of the rhodium, resulting in a stable rhodium-bisphosphite complex. In principal, the remaining rhodium is ligated by the bulky monophosphite; however, rhodium-bulky monophosphite complexes form at a relatively slow rate under hydroformylation conditions. Thus, in a reactor charged with rhodium and a bulky monophosphite alone or with a bulky monophosphite and a substoichiometric amount of bisphosphite, some portion of the rhodium may not initially be ligated. This results in a situation where valuable rhodium may be deposited or lost in parts of the process.
Increasing the concentration of the bulky monophosphite might appear to be a solution to this problem. However, many preferred bulky monophosphites are only modestly soluble in the reaction matrix, which limits their final concentration. Additionally phosphite ligand degradation reactions are typically positive order (i.e., the more ligand present, the faster it decomposes), which creates operational issues and increases cost when using a large excess of ligand. Thus, there exists a need for an improved process for forming a hydroformylation catalyst, which process would reduce the risk of losing valuable rhodium and reduce the risk of accelerated ligand degradation.